Changes since RFC: - Call kvm_put_msr_feature_control() before kvm_put_sregs2() to achieve the same result [Paolo]. - Add Maxim's R-b to PATCH1.
It was discovered that Windows 11 with WSL2 (Hyper-V) enabled guests fail to reboot when QEMU's 'system_reset' command is issued. The problem appears to be that KVM_SET_SREGS2 fails because zeroed CR4 register value doesn't pass vmx_is_valid_cr4() check in KVM as certain bits can't be zero while in VMX root operation (post-VMXON). kvm_arch_put_registers() does call kvm_put_nested_state() which is supposed to kick vCPU out of VMX root operation, however, it only does so after kvm_put_sregs2() and there's a good reason for that: 'real' nested state requires e.g. EFER.SVME to be set. The root cause of the issue seems to be that QEMU is doing quite a lot to forcefully reset a vCPU as KVM doesn't export kvm_vcpu_reset() (or, rather, it's super-set) yet. While all the numerous existing APIs for setting a vCPU state work fine for a newly created vCPU, using them for vCPU reset is a mess caused by various dependencies between different components of the state (VMX, SMM, MSRs, XCRs, CPUIDs, ...). It would've been possible to allow to set 'inconsistent' state and only validate it upon VCPU_RUN from the very beginning but that ship has long sailed for KVM. A new, dedicated API for vCPU reset is likely the way to go. Resolve the immediate issue by setting MSR_IA32_FEATURE_CONTROL before kvm_put_sregs2() (and kvm_put_nested_state()), this ensures vCPU gets kicked out of VMX root operation. Vitaly Kuznetsov (2): i386: reset KVM nested state upon CPU reset i386: do kvm_put_msr_feature_control() first thing when vCPU is reset target/i386/kvm/kvm.c | 54 +++++++++++++++++++++++++++++++------------ 1 file changed, 39 insertions(+), 15 deletions(-) -- 2.37.1
